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SYNOPSISStudies on electrochemical polymerization of pyrrole in the presence of thiophene are given for preparation of polypyrrole (PPy)/polythiophene (PTh) double layers. At a constant current, only pyrrole is electrochemically polymerized in the electrolytic solution containing pyrrole and thiophene in the present experiments. The cyclic voltammograms on pyrrole/ thiophene mixtures are similar to that on pyrrole. Preparation of PPy/PTh double layers is carried out by electrochemical polymerization of pyrrole in the presence of thiophene by adding pyrrole and by lowering voltage immediately after electrochemical homopolymerization of thiophene. The resulting double layers show good rectification characters dependent on thickness. 0 1995 John Wiley & Sons, Inc. INTRODUCTIONElectrochemical polymerization may facilitate preparation of conductive organic polymers. Among many organic compounds, aromatic heterocyclic compounds such as pyrrole and thiophene are subject to electrochemical p~lymerization.'-~ These polymers have a high potential for use in electronic devices. There are some report^^-^ concerning applications of these polymers to electronic devices. Kaneto et a1.6 succeeded in preparing a polythiophene (PTh)/polypyrrole (PPy) heterojunction, by electrochemical polymerization of thiophene on a PPy film which was polymerized in another electrolytic cell (although we were unable to polymerize electrochemically thiophene on a PPy filmt). The change of the electrolytic cell in this preparation is attended by air oxidation, which may account for this. To avoid this oxidation, we examined two methods for the preparation of PPy/PTh double layers without change of the electrolytic cell. In one method (method l), galvanostatic copolymerization of pyrrole with thiophene was examined, since we expected that pyrrole would be polymerized until consumption of the total amount of pyrrole in the feed and then thiophene would be polymerized, in an electrolytic cell involving pyrrole and thiophene at a constant current. In another method (method 2), electrochemical polymerization of pyrrole in the presence of thiophene was carried out by adding pyrrole and by lowering voltage immediately after the electrochemical homopolymerization of thiophene. In these methods mentioned above, pyrrole needs to polymerize electrochemically in preference to thiophene in the electrolytic solution containing pyrrole and thiophene.Electrochemical copolymerizations of monomers with mutually similar oxidation-reduction potentials such as pyrrole and substituted pyrrole have been However, studies of electrochemical copolymerization of monomers with mutually different oxidation-reduction potentials such as pyrrole and thiophene, to our knowledge, have not been reported. Therefore, we studied also cyclic voltammetry on pyrrole/thiophene mixtures to obtain basic data on electrochemical polymerization of pyrrole in the presence of thiophene.* To whom correspondence should be addressed.' The causes will be described elsewhere. EXPERIMENTALmersing them...

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